Liquid crystal displays, operational on relatively low electric power, are found in a wide range of applications from mobile to stationary devices. In comparison to the cathode-ray tube (CRT), the liquid crystal display is slow to respond, hence to change tone, and may fail to respond completely within a rewrite time (16.7 msec) corresponding to an ordinary frame frequency (60 Hz), i.e., frame period. US 2002/0044115 A1 published on Apr. 18, 2002, a counterpart of Japanese Published Unexamined Patent Application or Tokukai 2002-116743, suggests a method addressing this issue which modulates drive signals for quick transition from the current tone to the desired tone.
For example, suppose that the tone transition from the current frame FR(k−1) to the desired frame FR(k) requires a “rise” drive. If so, a higher voltage than that represented by the video data D(i, j, k) for the desired frame FR(k) is applied to a pixel, so as to facilitate the transition from the current tone to the desired tone.
In tone transition, the application of such a voltage increases the brightness level of the pixel more abruptly and takes less time to raise it to the proximity of the brightness level in accordance with the video data D(i, j, k) for the desired frame FR(k) than the application of an exact voltage represented by the video data D(i, j, k) for the desired frame FR(k). Thus, the liquid crystal display will have a fast response speed despite the slow response speed of the liquid crystal.
However, suitable tone transition facilitation may become impossible for a desired frame if the tone transition is facilitated presuming that transition is sufficiently performed from the current tone to the desired tone, despite the fact to the contrary, i.e., a targeted brightness level is actually not reached in the transition from the current tone to the desired tone despite such driving that the tone transition is facilitated to overcome insufficient liquid crystal response speed.
For example, when the liquid crystal is driven so that the transition from the previous tone through the current tone to the desired tone (transition from the previous tone to the current tone and transition from the current tone to the desired tone) is a “decay” followed by a “rise” as indicated in a solid line in FIG. 12, if the liquid crystal response speed is fast enough, sufficient tone transition occurs as indicated by a dash-dot line in the figure. In some cases, however, the transition from the previous tone to the current tone is so insufficient that the brightness level does not sufficiently drop at the end of the current frame FR(k−1) as indicated by a broken line in the figure. If the pixel is driven in the desired frame FR(k) with enhanced tone transition similarly to the case of sufficient tone transition in such cases, the tone transition is enhanced too much and causes excess brightness.
When the liquid crystal is driven so that the transition from the previous tone through the current tone to the desired tone is a “rise” followed by a “decay” as indicated by a solid line in FIG. 13, if the liquid crystal response speed is fast enough, sufficient tone transition occurs as indicated by a dash-dot line in the figure. In some cases, however, the transition from the previous tone to the current tone is so insufficient that the brightness level does not sufficiently “rise” at the end of the current frame FR(k−1) as indicated by a broken line in the figure. If the pixel is driven in the desired frame FR(k) with enhanced tone transition similarly to the case of sufficient tone transition in such cases, the tone transition is enhanced too much and causes inadequate brightness.
When the liquid crystal is driven so that the transition from the previous tone through to the desired tone is a “decay” followed by another “decay” as in indicated by a solid line in FIG. 14, if the liquid crystal response speed is fast enough, sufficient tone transition occurs as indicated by a dash-dot line in the figure. In some cases, however, the transition from the previous tone to the current tone is so insufficient that the brightness level does not sufficiently drop at the end of the current frame FR(k−1) as indicated by a broken line in the figure. In these cases, the liquid crystal response speed in the desired frame FR(k) tends to slow down.
Similarly, when the liquid crystal is driven so that the transition from the previous tone through to the desired tone is a “rise” followed by another “rise” as indicated by a solid line in FIG. 15, if the liquid crystal response speed is fast enough, sufficient tone transition occurs as indicated by a dash-dot line in the figure. In some cases, however, the transition from the previous tone to the current tone is so insufficient that the brightness level does not sufficiently “rise” at the end of the current frame FR(k−1) as indicated by a broken line in the figure. In these cases, the liquid crystal response speed in the desired frame FR(k) tends to slow down.
Addressing the same problems, Japanese Patent No. 2650479 (published on Sep. 3, 1997) corrects signal data applied to the liquid crystal throughout the two or more fields after the first signal data. The scheme requires that video data for multiple fields be stored, and will likely add to the circuit dimensions.
As detailed in the foregoing, according to US 2002/0044115 A1, the display element does not have a sufficient response speed. If tone transition is enhanced similarly to the case of sufficient tone transition despite the actual fact that tone transition is insufficient, the tone transition is enhanced too much and may degrade the display quality of the display.
Meanwhile, Japanese Patent No. 2650479 requires that video data for multiple fields be stored, and will likely add to the circuit dimensions. This is especially true when it is considered that many displays are required to increase its number of pixels and tones to produce a more natural and smooth image.